PRIOR CONCURRENT THERAPY: Biologic therapy: No concurrent prophylactic growth factors (e.g., filgrastim (G-CSF)) Chemotherapy: No more than 1 prior chemotherapy regimen as adjuvant therapy or for recurrent disease At least 6 weeks since prior chemotherapy Endocrine therapy: Stable or decreasing dose of corticosteroids for at least 1 week prior to study Radiotherapy: At least 3 months since prior radiotherapy to the brain No prior high-dose radiotherapy (more than 65 Gy), stereotactic radiosurgery, or internal radiotherapy unless the disease recurrence is histologically confirmed Surgery: No prior surgery (except biopsy) for recurrent brain tumor At least 3 months since prior surgery for primary brain tumor Other: No other concurrent anticancer agents No other concurrent investigational agents